Gas generator

ABSTRACT

A gas generator has a propellant charge and an early ignition device held loosely in the propellant charge. The early ignition device consists of an early ignition charge and an enclosure surrounding the early ignition charge. The enclosure is at least one foil wrapped around the early ignition charge. The outer edges of the foil, lying one over another, are connected with each other to close the enclosure.

FIELD OF THE INVENTION

The invention relates to a gas generator.

BACKGROUND OF THE INVENTION

In gas generators which are to be used in vehicle safety systems, the German Federal Institute for Materials Research and Testing prescribes a specific auto-ignition behaviour. Thus, for example, the gas generator must activate itself in the case of a possible vehicle fire, so that the propellant contained in it burns without risk to vehicle occupants and rescuers. For this purpose, it is known to provide an early ignition device (also called auto-ignition device) in the gas generator, which is ignited from the exterior by the action of heat and therefore not via the normal ignition chain which is passed through in an activation caused by an accident. This early ignition device then ignites the main propellant charge of the gas generator so that all the pyrotechnic material in the gas generator burns.

The early ignition device is often integrated especially into the design of a specific gas generator, which is very complex and increases the development costs for the gas generator.

BRIEF SUMMARY OF THE INVENTION

It is an object of the invention to provide a gas generator with a universally usable early ignition device.

This object is achieved by a gas generator that has a propellant charge and an early ignition device held loosely in the propellant charge. The early ignition device consists of an early ignition charge and an enclosure (i.e. a casing) surrounding the early ignition charge.

The early ignition charge directly contacts the inner side of the enclosure whereas the main propellant charge contacts the outer side of the enclosure. By encapsulating the early ignition charge in an enclosure, early ignition devices can be produced which may be used in the propellant bed of any desired gas generator. The enclosure also protects the early ignition charge to a certain extent from mechanical wear and from moisture.

Furthermore, on ignition of the early ignition charge a certain pressure initially builds up inside the enclosure, until the enclosure bursts. In this way, the combustion of the early ignition charge, which in fact takes place at relatively low ignition temperatures, is improved and a distinctly improved over-igniting onto the main propellant charge is achieved. The enclosure facilitates a combination of early ignition propellant and ignition propellant. By the shared accommodation in one chamber and the direct contact of the early ignition propellant with the ignition propellant, the ignition energy is increased compared with a separate arrangement of the early ignition propellant. The over-igniting to the ignition propellant is also improved.

The enclosure preferably consists of a material which is chemically inert with respect to the material of the propellant charge, so that the pairing of material of early ignition charge/propellant charge can be selected completely freely. As the enclosure separates the early ignition charge from the actual propellant charge, it is not important whether the early ignition charge and the material of the propellant charge are chemically compatible. Accordingly, a much wider range of early ignition propellants can be used than would be the case in conventionally known early ignition tablets arranged loosely in the propellant charge, or a granulate mixture.

It is a further object of the invention to provide an early ignition device.

This is achieved in an early ignition device that consists of an early ignition charge and an enclosure surrounding the early ignition charge. The enclosure is at least one foil wrapped around the early ignition charge. The outer edges of the foil, lying one over another, are connected with each other to close the enclosure. Of course, this technique can be carried out both with a single foil piece and also with two or more individual foil pieces. This early ignition device is quick and simple to produce, even in the case of small filling quantities for the early ignition charge.

In one preferred embodiment, the early ignition charge can be wrapped for example into a foil piece, the edges of which are folded onto each other. The enclosure which is thus formed is closed by the outer edges of the foil piece, which lie one over the other, being connected. It is also possible to use two separate foil pieces, between which the early ignition charge is arranged and which are connected with each other at the edges around the early ignition charge.

In one possible embodiment, the closing of the enclosure takes place at at least one end by a weld seam. This is possible, despite the proximity to the early ignition charge, because owing to the thin gauge of foil which can be used, only a very short influence by heat is necessary.

According to another embodiment, the enclosure is closed at at least one end by beading or by crimping. Here, the outer edges of the foil, which lie one over another, are folded over or rolled in.

It is also possible to close the outer edges of the foil by stamping or by glueing with a suitable adhesive.

Of course, the methods can also be combined with each other, so that for example particular sections of the outer edges of the foil are closed by one method, and other sections of the outer edges are closed by other methods.

Instead of a foil piece, a prefabricated foil container can also be used, which only has one axially open end which-is closed, preferably by crimping or beading, after filling with the early ignition charge.

The enclosure may consist, for example, of a metal foil, which offers the advantage of good heat transmission to the early ignition charge. However, it is also possible to form the enclosure from a plastic, which facilitates the selection of a material which is inert with respect to the propellant charge and/or to the early ignition charge.

It is also possible that the enclosure consists of a laminate foil, e.g. a metal foil laminated with plastic, or else a paper laminated with plastic or metal.

The early ignition charge preferably contains a portion of an early ignition propellant and a portion of an ignition propellant: therefore consists of a mixture of an early ignition propellant and an ignition propellant.

The early ignition charge can contain for example at least one tablet of the early ignition propellant and at least one tablet of the ignition propellant. The production of the early ignition device in this case is extremely simple. The corresponding number of tablets of the early ignition propellant and respectively of the ignition propellant are simply packed in the foil enclosure.

Alternatively, it is possible that the early ignition charge is formed by a granulate mixture of the early ignition propellant and the ignition propellant, in which this mixture can also be produced simply in advance and filled into the foil.

A third alternative would be to compress the early ignition charge to form tablets which contain both ignition propellant and also early ignition propellant, and to pack one or more of these tablets in the foil.

SHORT DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a view, partially in section, of a gas generator according to the invention, with an early ignition device according to the invention;

FIG. 2 shows a diagrammatic sectional view of an embodiment of an enclosure for an early ignition device according to the invention;

FIG. 3 shows a first embodiment of an early ignition device according to the invention;

FIG. 4 shows an early ignition device according to the invention during a welding process;

FIG. 5 shows a second embodiment of an early ignition device according to the invention;

FIG. 6 shows a perspective view of a third embodiment of an early ignition device according to the invention;

FIGS. 7 a and b show an early ignition device according to the invention with a first type of early ignition charge, in section and respectively in perspective view;

FIG. 8 shows the early ignition device in FIG. 7 with a second type of early ignition charge; and

FIG. 9 shows the early ignition device in FIG. 7 with a third type of early ignition charge.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

The gas generator 10 shown in FIG. 1 is a cup-shaped gas generator, as is used for example for driver's gas bags in passenger cars.

In addition to other components usually contained in gas generators of this type, which are not described in further detail here, the gas generator 10 has a metallic outer housing 12, into which an igniter 14 is inserted, by means of which the gas generator 10 is activated by a control unit (not shown) in the case of an accident (following the normal ignition chain). The igniter 14 ignites a propellant charge 16 of fuel tablets, which is loosely filled in a combustion chamber 18.

An early ignition device 20 is loosely introduced into this propellant charge 16. The early ignition device 20 serves for an auto-ignition of the gas generator 10, if the latter is exposed to an increased ambient temperature for a prolonged period of time (e.g. under the conditions of a bonfire test), as is required by the BAM. In such a case, initially the early ignition device 20 ignites, independently of the normal ignition chain, which then causes a controlled burning of the propellant charge 16, so that the pyrotechnic material burns without danger in the gas generator 10.

In all the embodiments shown here, the early ignition device 20 consists of an enclosure 22 and an early ignition charge 24 enclosed by the enclosure 22.

The enclosure 22 preferably encloses the early ignition charge 24 hermetically. It separates it chemically from the propellant charge 16. In addition, it offers resistance to a certain pressure rise in its interior, so that when the early ignition charge 24 burns, initially a certain pressure builds up in the interior of the enclosure 22, before the enclosure 22 bursts and burning particles of the early ignition charge 24 and hot gases come in contact with the propellant charge 16, in order to ignite it.

The enclosure 22 can consist of any suitable foil material. Here, for example, aluminium foil, plastic foils, but also laminate foils of metals coated with plastic, plastics coated with metal, or other suitable combinations, are to be mentioned.

The foil preferably has a maximum thickness of 0.4 mm and is highly flexible.

The foil piece forming the enclosure 22 can be in one piece and in the initial state can be formed into a bag which is open only at one end, or can be spread out flat (see FIGS. 2 to 6).

In the embodiment of an early ignition device 20 a illustrated in FIGS. 2 and 3, a prefabricated bag is provided, which is closed on three sides, to produce the enclosure 22. The early ignition charge 24 is filled into this bag and then the free end is closed.

Suitable dimensions for such a bag would be, for example, an opening diameter d₁ of 6 mm, with an enclosure length I of 15 mm and a foil thickness d₂ of 0.3 mm.

In the example shown in FIG. 3, the free outer edges 26 are placed one on another and rolled in, i.e. beaded, after the filling of the early ignition charge 24. They could also be crimped, or can undergo a combination of rolling, folding and crimping processes, folded over or beaded.

The free outer edges 26 can also be welded to each other, as is shown in FIG. 4 for the early ignition device 20 b. FIG. 5 shows a section through an early ignition device 20 b which is produced in such a way. Here, in order to avoid a sparkover from the welding electrodes 28 to the early ignition charge 24, additional cheek pieces 30 are used to enlarge the spacing, which cheek pieces 30 lie between the enclosure 22 and the welding electrodes 28.

Instead of an electro-welding process, ultrasonic welding can of course be used. In this case, a plastic- or a laminate foil with a plastic component can also be used instead of a metal foil.

In the simplest case of an early ignition device 20 c, which is illustrated in FIG. 6, the enclosure 22 is formed from a single, flat foil piece, onto which the early ignition charge 24 is placed. The halves of the foil piece are folded together over the early ignition charge 24, and the outer edges 26 of the foil piece are connected with each other, where they lie one over the other, in order to close the enclosure 22.

The connecting of the outer edges 26 can take place for example by welding or stamping, in which a shape similar to a sugar sachet can be produced.

The early ignition device 20 c is produced in the manner of a sugar sachet. Here, the early ignition charge 24 is wrapped into a foil piece, consisting of a single piece, and the three outer edges 26 of the foil piece which lie one over the other are connected with each other, e.g. by stamping, welding or beading. The dimensions can be similar to as described in FIG. 2.

It is also possible to use several, e.g. two, foil pieces, as is shown in the embodiment of FIGS. 7 to 9 and is described in further detail there.

Here, the enclosure 22 of the early ignition device 20 d consists of two separate foil pieces, the outer edges 26 of which are connected in a ring shape around the early ignition charge 24 lying therebetween.

In the example embodiments described here, the early ignition charge 24 is always composed of a mixture with a predetermined proportion of an early ignition propellant 32 and a predetermined proportion of an ignition propellant 34, e.g. in a total amount of approximately 200 mg.

Suitable substances for the ignition propellant are, for example, pyrotechnic mixtures of boron, KNO₃, guanidine nitrate, KClO₄, Al, 5-aminotetrazol, basic copper nitrate, copper oxide, strontium nitrate. Suitable early ignition propellants are pyrotechnic mixtures based on nitrocellulose, NTO, KNO₃, KClO₄, carbon etc.

In the variant shown in FIG. 7, the mixture of ignition propellant and early ignition propellant is held as a granulate loosely in the enclosure 22. The early ignition charge 24 is also shown in this form in FIGS. 3, 4 and 5.

In the variant illustrated in FIG. 8, the mixture of early ignition propellant 32 and ignition propellant 34 is compressed into a single tablet 38, which is again surrounded by the enclosure 22.

In the variant shown in FIG. 9, one tablet of the early ignition propellant 32 and one tablet of the ignition propellant 34 are surrounded together in the enclosure 22. Of course, several tablets of the early ignition propellant and/or of the ignition propellant 34 could also be used here.

All the features of the shown and described embodiments can be freely combined with each other or exchanged for each other at the discretion of the specialist in the art. Above all, the various types of connection of the outer edges 26 of the enclosure 22 can also be combined within an early ignition device. Thus, a single enclosure 22 could have glued, beaded, stamped, crimped and/or welded edge sections.

The early ignition devices 20 a, 20 b, 20 c could also equally well be filled with tablets as shown in FIG. 8 or FIG. 9, instead of with a granulate. 

1. A gas generator with a propellant charge (16) and with an early ignition device (20-20 d) held loosely in the propellant charge (16), the early ignition device (20-20 d) consisting of an early ignition charge (24) and an enclosure (22) surrounding the early ignition charge (24).
 2. The gas generator according to claim 1, wherein the enclosure (22) consists of a material which is chemically inert with respect to the material of the propellant charge (16).
 3. An early ignition device for a gas generator, wherein the early ignition device (20-20 d) consists of an early ignition charge (24) and an enclosure (22) surrounding the early ignition charge (24), in which the enclosure (22) is at least one foil wrapped around the early ignition charge (24), the outer edges (26) of which foil, lying one over another, are connected with each other to close the enclosure (22).
 4. The early ignition device according to claim 3, wherein the enclosure (22) is closed by a weld seam at least at one end.
 5. The early ignition device according to claim 3, wherein the enclosure (22) is closed by beading, folding or crimping at at least one end.
 6. The early ignition device according to claim 3, wherein the enclosure (22) consists of a metal foil.
 7. The early ignition device according to claim 3, wherein the enclosure (22) consists of a plastic.
 8. The early ignition device according to claim 3, wherein the enclosure (22) consists of a laminate foil.
 9. The early ignition device according to claim 3, wherein the early ignition charge (24) contains a portion of an early ignition propellant (32) and a portion of an ignition propellant (34).
 10. The early ignition device according to claim 9, wherein the early ignition charge (24) contains at least one tablet of the early ignition propellant (32) and at least one tablet of the ignition propellant (34).
 11. The early ignition device according to claim 9, wherein the early ignition charge (24) is formed by a granulate mixture of the early ignition propellant (32) and the ignition propellant (34).
 12. The early ignition device according to claim 9, wherein the early ignition charge (24) is compressed to a single tablet. 